On Tue, 26 Oct 1999 04:09:09 -0700, Ken wrote:
>
>
>2. (Fine Arts) The color or incrustation which age gives to works of art;
>especially, the green rust which covers ancient bronzes, coins, and medals.
>
> It is quite common to see a patina discoloration inside the cracks,
>crevices, and deep folds on sculpture while it's surface maintains
>more of the original material's coloration.
>
> How would one apply this affect to a 3d object with proceedural methods
>rather than relying upon complicated image maps ?

I have a SIGGRAPH article on just this subject.  Combined with the reference
Thomas posted, it should do just what you want.  The article is called
"Efficient Algorithms for Local and Global Accessibility Shading" and is
by Gavin Miller.  It was published in the SIGGRAPH 1994 Proceedings, but 
is not available online.  It talks about how to texture objects based on 
their accessibility to cleaning agents - deep ridges and cracks don't get
cleaned as effectively so they gather dirt (or corrosion) over time.

If someone wants to try to implement the techniques in this article, I'd
be happy to scan it and email it to one or two people.  That's in the scope
of the ACM's copyright notice, I believe.  Be warned that it isn't very 
well suited to general objects like those in POV.  It does have some good 
suggestions for heightfields, spheres, and meshes, though.

And, just to satisfy your lust for links, here's one everyone should know:

http://www2.iro.umontreal.ca/~ratib/code/cg.htm

Besides the content, this link is interesting because it lets you link 
deeply but it uses Javascript to reconstruct the original frame structure.
While you're there, pay special attention to the link for Computer Graphics
Publications - that's where I got the title info for this paper (I have the
Proceedings at home.)

(That one should keep even The Great Ken busy for a few hours...)

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